The disclosure is based on a carbon brush with disconnection apparatus according to the description below.
Carbon brushes of this type are known (DE 1 679 529 U1) in which the compression-spring body consists of a cylindrical helical spring, which, in order to achieve the lowest possible overall length of the system of the disconnection apparatus and the greatest possible wear travel of the brush body, can be prestressed and compressed at most to such an extent that the cylindrical turns thereof rest on one another and the spring is prestressed to form a block. This thus leads to a relatively great axial length of such a compression-spring body. On account of the latter, a small usable wear travel of the brush body remains, which results from the ratio of the possible theoretical wear travel of the carbon brush to the length of the disconnection apparatus. A low wear travel as a real useful length of the brush body requires early replacement of the carbon brushes when the latter have exceeded the permissible wear travel. A further disadvantage lies in the fact that cylindrical helical springs, as compression-spring bodies, have a low flexural rigidity. During the disconnection operation, when the compression-spring body has already lifted the brush body off the commutator of an electric motor and has interrupted the power circuit, the electric motor continues to run down. In the case of unbraked machines at idle, this running down can last for 5 to 15 seconds. During this time, transverse forces act on the compression-spring body as a result of the contact of the disconnection body with the rotating commutator, which may lead to severe misalignment of the cylindrical helical spring and to the disconnection body tearing out as a result of this severe misalignment.